Question: William is 16 years older than Tiffany. Three years ago, William was 5 times as old as Tiffany. How old is Tiffany now?
Answer: We can use the given information to write down two equations that describe the ages of William and Tiffany. Let William's current age be $w$ and Tiffany's current age be $t$ The information in the first sentence can be expressed in the following equation: $w = t + 16$ Three years ago, William was $w - 3$ years old, and Tiffany was $t - 3$ years old. The information in the second sentence can be expressed in the following equation: $w - 3 = 5(t - 3)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $t$ , it might be easiest to use our first equation for $w$ and substitute it into our second equation. Our first equation is: $w = t + 16$ . Substituting this into our second equation, we get the equation: $(t + 16)$ $-$ $3 = 5(t - 3)$ which combines the information about $t$ from both of our original equations. Simplifying both sides of this equation, we get: $t + 13 = 5 t - 15$ Solving for $t$ , we get: $4 t = 28$ $t = 7$.